This invention relates to disc brakes in general, but in particular to disc brakes for vehicles. It is intended to alleviate the problem of maintaining a safe ratio between the braking effort at the front and rear of the vehicle in spite of the variations in the coefficient of sliding friction at the brake shoes. A further object of this invention is to maintain an adequate and effective brake torque even with unfavorable conditions of brake shoe friction.
In order to insure that braking torques on front and rear wheels are properly proportioned to avoid unsymmetrical wheel locking and car skidding, means such as a proportioning valve are used to distribute the hydraulic brake actuating force at the front and rear wheels so as to maintain a fixed ratio of rear to front brake torques. However, such means are made less effective if the coefficient of sliding friction between the brake shoe and disc varies in a random and unpredictable manner due to such factors as corrosion, wear, or moisture, and other chemical and physical changes.